CurrencyField is an advanced field type indexing a monetary value as both value and currency. It lets e.g. an e-commerce site display and query prices in many currencies, while only indexing the price in one field/currency.
The field type is backed by a pluggable ExchangeRateProvider. The provider shipping with Solr as default is the FileExchangeRateProvider. Changes in exchange rates from the provider does not require re-indexing, since all conversions are done query-time. You simply choose for each document which currency to index, and this will be fixed.
Configuration
See example schema for example of how to use the field type. The field type and field is defined in schema.xml as follows:
<fieldType name="currency" class="solr.CurrencyField" precisionStep="8" currencyConfig="currency.xml" defaultCurrency="EUR" /> <dynamicField name="*_c" type="currency" />
DefaultCurrency will be used if you do not specify a currency. The default defaultCurrency is USD, if not specified. Note that defaultCurrency cannot be changed unless followed by a full re-index. PrecisionStep is passed on to the TrieLong sub-field. Value "8" gives faster range queries for currencies. If you don't need that, you can save some index space using "0".
Indexing
When you index e.g. a price, you specify value and currency separated by comma. We use the dynamicField *_c in our examples:
<doc> <field name="id">1</field> <field name="myprice_c">1.00,USD</field> </doc>
Here, 1.00,USD is assumed to mean $1.00. Note that regardless of the currency being indexed, you must encode the value as a floating point value (with a decimal point.) The fractional portion of the floating point value is interpreted based upon the currency, via Currency.getDefaultFractionDigits().
Querying
The CurrencyField supports both point queries and range queries. Here are some valid money queries. Assume default currency is USD. In the example schema there is a copyField from "price" to "price_c", meaning that you can test this on the example data:
price_c:25.00,USD or price_c:25.00 Both of these will query for USD 25.00 since USD is default price_c:[* TO 10.00,USD] or price_c:[* TO 10.00] price_c:[10.00,EUR TO 100.00,EUR] price_c:10.00,NOK
ExchangeRateProviders
You may plug in your own provider class through implementing the interface ExchangeRateProvider. It may be backed by a web-service, by a flat file, a DB or what have you.
You specify which provider class to use through the parameter providerClass on the fieldType. If no provider is specified in the fieldType config, FileExchangeRateProvider is used as default.
FileExchangeRateProvider
This provider is backed by an XML file currency.xml, and a fieldType using this provider. It requires one parameter currencyConfig which should point to your XML file. This config is looked up through Solr's ResourceLoader.
The example currency.xml file in "conf" folder shows how the config could look. Here's an example:
<currencyConfig version="1.0">
<rates>
<!-- Example -->
<rate from="USD" to="JPY" rate="81.29"/>
<!-- Fake rates for testing -->
<rate from="USD" to="EUR" rate="2.5"/>
<rate from="USD" to="GBP" rate="0.5"/>
<rate from="EUR" to="GBP" rate="0.5"/>
<!-- Asymmetric rate -->
<rate from="EUR" to="USD" rate="0.5"/>
</rates>
</currencyConfig>Note that you need a rate entry between every two pairs of currencies you will index or query. So if you handle USD, EUR and GBP, you need USD->EUR, USD->GBP and EUR->GBP, so that all possible conversions can be done. If you only index one currency (say USD) but want to query or convert multiple, it is enough to have rates between USD and all currencies you'll query or display.
By default the rate will be symmetrical, but you may override this by explicitly specifying the reverse rate.
Replication is supported, given that you explicitly configure replication for currency.xml. Upon the arrival of a new version of currency.xml, Solr slaves will do a core reload and begin using the new exchange rates. See SolrReplication for more. SolrCloud is also supported since we use ResourceLoader to load the file.
OpenExchangeRatesOrgProvider
This provider downloads and parses the freely available exchange rates from openexchangerates.org, giving rates between USD and 158 currencies, updated hourly. The rates are symmetrical only. Rates between any two currencies are calculated using USD as common base. Sample fieldType configuration:
<!-- Money/currency field type. See http://wiki.apache.org/solr/MoneyFieldType
Parameters:
defaultCurrency: Specifies the default currency if none specified. Defaults to "USD"
precisionStep: Specifies the precisionStep for the TrieLong field used for the amount
providerClass: Lets you plug in other exchange provider backend:
solr.FileExchangeRateProvider is the default and takes one parameter:
currencyConfig: name of an xml file holding exhange rates
solr.OpenExchangeRatesOrgProvider uses rates from openexchangerates.org:
ratesFileLocation: URL or file path to rates JSON file (default latest.json on the web)
refreshInterval: Number of minutes between each rates fetch (default: 1440, min: 60)
-->
<fieldType name="currency" class="solr.CurrencyField" precisionStep="8"
providerClass="solr.OpenExchangeRatesOrgProvider"
refreshInterval="60"
ratesFileLocation="http://internal.server/rates.json"/>This tells the CurrencyField to use the OpenExchangeRates provider with the rates JSON file loaded from a local web server, refreshed every hour. The defaults are using the latest rates file from http://openexchangerates.org/latest.json, refreshed once every day.
NOTE: You can use this provider in Solr3.6 as well by downloading the plugin jar file from SOLR-3255 and adding it to your classpath.
Usage
Solr documents will always yield the currency values they were indexed with, regardless of how they were queried for. For example, a set of documents indexed in USD will yield USD values for its Currency fields regardless if you performed queries in EUR.
So, for the display of Currency fields to a user, it is often necessary to perform a second currency conversion once the documents are returned for display purposes. For accuracy, this conversion should apply the same exchange rates in the currency.xml file available to Solr.
TODO
facet.range is not yet supported for this field type - See SOLR-3218